This is what veb's flames look like:
Kinda hard to see cos of the white background, but the flames are white and multicoloured.
Just like in this pic:
Obviously the set would have a gradient of transparency from the hands up the arms, and from the feet up the legs, and also a brightness gradient, so it looks like the figure is ascending.
Seems there is no real guidlines on the figure, but i would go with a semirealistic manga style.